1. Field of the Invention
This invention relates to an apparatus for removing granular material from a sewage treatment plant. More specifically, this invention relates to an apparatus for removing sand from an aeration basin of a sewage treatment plant or the like.
2. Information Disclosure Statement
Municipal waste or the like is conveyed to a local sewage treatment plant in which the raw sewage is treated in various sedimentation processes after which the primary sludge is further treated in an aeration tank or basin for biological degradation thereof.
Although most sewage treatment plants incorporate bar screens and grit chambers for removing entrained granular material from the sewage to be treated, in practice a considerable amount of granular material reaches the aeration basin where such granular material accumulates.
The primary function of the aeration basin or aeration tank is to supply a steady stream of oxygen through the sewage contained in the aeration basin. Such oxygen enhances the ability of bacteria comprising the bio-mass within the aeration basin to feed upon and thereby degrade and decompose the sewage.
However, as the level of granular material accumulates within the aeration basin, the effective depth of the basin decreases. Therefore, the flow path of the air through the sewage aeration basin becomes shortened as the granular material accumulating within the aeration basin increases. This decrease in the distance travelled by the air through the sewage to be treated reduces the efficiency with which the sewage may be treated by such oxygen and this results in the requirement for more air for longer periods of time to compensate for the decrease in efficiency of the system as the granular material displaces the capacity of the aeration tank.
Another problem encountered with the accumulation of granular material within the aeration basin is that occasionally such accumulated solids will break loose and will travel downstream from the aeration basin and actually plug air defusers and the like thereby reducing the efficiency of the aeration process. Furthermore, if such granular material is carried completely over into an adjacent treatment tank, plugging of perculation ponds or drain fields may occur.
Above all, due to the accumulation of sand or similar granular material at the base of the aeration basin, the overall cost of operating the sewage treatment plant will increase because not only will the capacity of the aeration basin be reduced thereby reducing the overall effectiveness of the plant, but also because sewage plants are subject to peak flows at certain hours of the day. These flow surges are normally buffered by the correct sizing of the aeration chamber or basin. However, when the aeration basin includes an accumulation of sand and other solids, this buffering effect is impaired and solids will pass through the aeration tank without being properly treated with the oxygen stream. Needless to say, authorities responsible for enforcing environmental regulations impose heavy fines on sewage treatment plant operators falling below regulatory standards.
When sand or the like accumulates within the base of an aeration basin, not only are greater loading requirements placed upon aeration equipment and ancillary pumping gear, but the reduced efficiency of the aeration tank requires greater amounts of chlorination to meet required regulations and all these associated inefficiencies result in a greatly increased cost when operating the sewage plant.
In the past, when sand or the like has accumulated in the bottom of an aeration tank, two alternative recourses have been available to the sewage plant operator. Firstly, the sewage may be diverted if practical to an alternative treatment plant while the sand is removed from the aeration chamber manually or secondly, the sewage contained within the aeration tank must be removed therefrom into transportation tanks for removal to an alternative plant. In either case, it is necessary to shut down the sewage plant while such removal of granular material from the aeration tank is carried out. Additionally, the removal of sand or similar granular material from the bottom of an aeration basin is a time consuming and unpleasant occupation, and results in removal of the beneficial biomass as well.
A need has existed in the art for an apparatus for removing such build-up of sand, grit or granular material from the base of an aeration tank while maintaining the continued operation of the sewage plant.
The present invention provides an apparatus which is completely self contained and which enables an operating crew to remove granular material from an aeration basin while such aeration basin is still filled with sewage, without interrupting the normal operation of the sewage plant.
The present invention overcomes the aforementioned inadequacies of the prior art device by the provision of a collector disposed within the aeration basin for collecting the granular material from the base of the basin and for pumping the granular material to a mobile reservoir where the granular material settles to the bottom of the reservoir and is conveyed by a separator for separating the granular material from the waste material and for pumping waste water and sewage back from the reservoir to the aeration basin.
Another object of the present invention is the provision of apparatus for removing sand or the like from an aeration basin in which the collector is manually positioned relative to the sand and grit at the base of the aeration basin.
Another object of the present invention is the provision of an apparatus for removing sand or the like from an aeration basin in which the collector is remotely positioned relative to the sand to be removed.
Another object of the present invention is the provision of an apparatus for removing sand or the like from an aeration basin in which the apparatus includes a float for supporting the collector at a variable depth relative to the granular material to be removed.
Another object of the present invention is the provision of an apparatus for removing sand or the like from an aeration basin including a buoyant conduit extending from the float to and over the rim of the aeration basin for removing the accumulated sand from the base of the aeration tank away from the aeration basin.
Another object of the present invention is the provision of an apparatus for removing sand or the like from an aeration basin including a reservoir disposed on a turntable rotatably secured to a truck such that sand or the like to be removed from the base of the aeration basin is conveyed to an inlet of the reservoir where the sand rapidly settles to the lower outlet of the reservoir.
Another object of the present invention is the provision of an apparatus for removing sand or the like from an aeration basin including a reservoir having sloping opposed walls which slope from the inlet towards the outlet of the reservoir for dissipating the turbulent energy of the slurry entering the reservoir.
Another object of the present invention is the provision of an apparatus for removing granular material from an aeration basin which includes an Archimedean screw conveyor having a first and a second end, the first end being disposed adjacent the outlet of the reservoir such that granular material and waste water is conveyed upwardly along an angularly disposed conveyor to separate the waste water from the sand or the like to be removed.
Another object of the present invention is the provision of an apparatus for removing granular material from an aeration basin in which the granular material is discharged from the second end of the Archimedean screw conveyor and waste water flows downwardly along the conveyor towards the reservoir.
Another object of the present invention is the provision of an apparatus for removing granular material from an aeration basin which includes a weir extending into the chamber of the reservoir for permitting the level of the slurry within the chamber to be limited.
Another object of the present invention is the provision of an apparatus for removing granular material from an aeration basin of a sewage treatment plant in which an accumulator is disposed between a weir and a second pump for accumulating the slurry flowing through the weir and for returning such slurry to the aeration basin.
The foregoing has outlined some of the more pertinent objects of the present invention. These objects should be construed as being merely illustrative of the some of the more prominent features and applications of the invention. Many other beneficial results can be obtained by applying the disclosed invention in a different manner or modifying the invention within the scope of the disclosure. Particularly with regard to the use of the invention disclosed herein, this should not be construed as being limited to an apparatus for removing granular material from a sewage treatment plant, but should include apparatus for removing granular material from drains, holding tanks, treatment tanks or the like.